Photodissociation dynamics of CF3CHO: C-C bond cleavage

The photodissociation dynamics of jet-cooled trifluoroacetaldehyde (CF3CHO) into radical products, CF3 + HCO, was explored using velocity mapped ion imaging over the wavelength range 297.5 nm <= lambda <= 342.8 nm (33 613-29 172 cm(-1)) covering the entire section of the absorption spectrum accessible with solar actinic wavelengths at the ground level. After initial excitation to the first excited singlet state, S-1, the radical dissociation proceeds largely via the first excited triplet state, T-1, at excitation energies above the T-1 barrier. By combining velocity-mapped ion imaging with high-level theory, we place this barrier at 368.3 +/- 2.4 kJ mol(-1) (30 780 +/- 200 cm(-1)). After exciting to S-1 at energies below this barrier, the dissociation proceeds exclusively via the ground electronic state, S-0. The dissociation threshold is determined to be 335.7 +/- 1.8 kJ mol(-1) (28 060 +/- 150 cm(-1)). Using laser-induced fluorescence spectroscopy, the origin of the S-1 <- S-0 transition is assigned at 28 903 cm(-1). The S-0 dissociation channel is active at the S-1 origin, but the yield significantly increases above 29 100 cm(-1) due to enhanced intersystem crossing or internal conversion. Published under an exclusive license by AIP Publishing.